This proposal for a Mentored Clinical Scientist Research Career Development Award (K08) describes a five year comprehensive training program leading to an academic career as in independent physician-scientist. The principal investigator has completed a Ph.D. program in molecular biology and biochemistry (at Rockefeller University), as well as medical training in internal medicine (at Columbia University) and nephrology (at Yale University). Now, he proposes to expand his training in cell and vascular biology through an intensive research experience. Dr. William Sessa, the Director of the Interdepartmental Program in Vascular Biology and Therapeutics at Yale and an internationally renowned vascular biologist will serve as mentor. Dr. Sessa has mentored multiple successful K awardees in the past, and more than a dozen of his former trainees currently hold independent research faculty appointments. In addition, an advisory committee of four highly-successful physician- scientists with a broad range of expertise in issues related to the project will provide regular advice on scientific and career development issues. Training will be rounded out through course work and attendance at lab meetings, research seminars, and external national and international meetings. Research will focus on the role of protein palmitoylation in endothelial cell biology. Past work in the mentor's laboratory has demonstrated the importance of palmitoylation of endothelial nitric oxide synthase in its localization and activity. In novel preliminary data, newly described proteomic techniques are used to show that the multifunctional endothelial cell protein PECAM is likely palmitoylated by a particular protein acyl transferase (PAT) known as DHHC-21. Additional preliminary data suggest that palmitoylation of PECAM by DHHC-21 is important for protein stability and localization. The specific aims include: 1) characterizing palmitoylation of PECAM by DHHC-21, 2) determining the consequences of DHHC-21-mediated palmitoylation on expression levels, stability, and localization of PECAM, and 3) characterizing the role of palmitoylation and of DHHC-21 on PECAM function. This project will address a dearth of knowledge about PAT-substrate interactions and about the importance of PECAM palmitoylation in endothelial cells. This work will be done at the crossroads of the section of nephrology at Yale, home to an array of accomplished physician-scientists, and the Program in Vascular Biology at Yale. This rich environment will furnish diverse scientific resources and interactions with numerous successful scientists. The environment and the proposed project provide excellent opportunity for the PI to develop a successful independent career as an academic physician-scientist.